minicom: add COPYING sha256 to hash

In minicom package hash file lacks sha256 entry for COPYING file even if
it is added to MINICOM_LICENSE_FILES.

Add COPYING sha256 entry to minicom.hash file.

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>